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It's funny how you start a "project" without really knowing it is to become a "project". I had always been interested in herps (reptiles and amphibians) since I was a small boy and I had always been fascinated by the sounds of the outdoors. I did start reading about recording wildlife/natural sounds in the early 1980s, but never pursued it because recording gear was expensive and onerous to take in the field.Around 2010, gear had not only come down in price (and my budget had increased since my undergrad days!), but it had become field hardy and accessible. So I dove in and bought a microphone (Sennheiser ME66/K6 and an Olympus LS-10 recorder). I started off recording a few birds around my house then expanded naturally to try, since I'm a herp guy, a few frog calls.Once I got a few recordings of common species around me (Blanchard's Cricket Frogs, Gulf Coast Toads, Great Plains Narrow-mouthed Toads) and I began to get comfortable with the process of recording and editing recordings, I thought "I wonder if I can get all the species that occur in my area", followed by "Hmm, it would be cool to get all the species that occur in my state".And so the project began. As I started collecting recordings from Texas, I had to opportunity to travel outside the boundaries of the state and the country so I took my recording gear with me....and my obsession began.So now my "goal" is to try and record as many species as I can. Yes there are good recordings of frog calls from many developed parts of the world, but they aren't always easy to access or can be expensive to buy. My goal was to provide a source of free recordings that people could use to help ID their frogs and toads. And mostly, I just enjoy doing it! 😁So here's my progress so far. I'm actually amazed I've managed to get this much stuff posted!

The White-lipped Frog (Leptodactylus fragilis) is a widespread frog from of the tropical lowlands from Southern Texas down into Panama and northern South America. Although it gets into Southern Texas, it is by no means common there and it may be one of the least often seen frogs in Texas.The difficulty of finding it in Texas is partly due to its limited range and period of activity, but also due to its habit of calling from partially flooded grassy areas where it may call from underneath clumps of grass or soil, or even from burrows underground. The frog photographed above was calling very loudly from an area of seemingly bare dirt with a few clumps of grass. I looked and looked and couldn't see it! Finally, I tracked it down to where it must be coming from and flipped a rock to find it calling from a burrow under the rock. Hopefully the females are better at tracking down males than I am! As a side note, I took this photo and took him back to the grass next to his rock. Within a few minutes, he had crawled back down his burrow and started calling again!The taxonomy of this frog has been confused in the literature over the years and it has been listed as Leptodactylus albilabris (which is restricted to Puerto Rico and the Virgin Islands) and Leptodactylus labialis which is not a valid name. Furthermore there is sometimes confusion with the South American species, Leptodactylus mystaceus.Although it is called a "white-lipped" frog, many individuals I have seen didn't seem to have a very conspicuous white lip at all?

The call of the White-lipped Frog is a upward whistle "pru-uh" sound repeated many times in a row. The call starts off around 900Hz and slurs quickly up to around 1.6kHz.

This individual was recorded just south of the town of La Palmera, Alajuela, Costa Rica in August 2014. As is typical with calling Leptodactylus species, the frogs were never seen.
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White-lipped Frog Call from Costa RicaHere is a recording from south of the town of Pisté, Yucatan, Mexico. This recording includes the individual above that was calling from underneath the rock as well as a couple of others that were calling from burrows.
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White-lipped Frog Calls from Yucatan, Mexico.

OK, so this blog post is going to start off with a correction to a previous blog post. My previous blog post about the Cane Toad (Rhinella marina) discussed the Cane Toad as being a species native to Texas, Mexico, Central America, South America and introduced to a variety of places worldwide. But a recent study based on mtDNA and skull morphology has shown that this "species" is actually two species of toad! So I am changing my old blog record to cover Rhinella marina and will make a new post for the Texas species, Rhinella horribilis.The Giant Toad (Rhinella horribilis) is a massive toad occuring from South Texas down into Mexico, Central America and along the northwest coast of South America (west of the Andes).

Giant Toad (Rhinella horribilis)Costa Rica

In Texas, this species is restricted to the lower Rio Grande Valley, occurring along the river and inland from Laredo down to the mouth of the Rio Grande. In South Texas it is a fairly common species.

Adult Cane ToadChiapas, Mexico

These are massive toads. Adults have exceeded 5 pounds in mass and been over 15 inches long.

The call of the Giant Toad is actually what you would expect for a huge toad. Toads generally have trilled calls. Smaller toads have faster, high-pitched trills and big toads have slower, low-pitched trills. The bigger the toad the lower pitched the trill. The trill of the Giant Toad is so slow and low pitched that it is drum-like. This individual was from north of Aguas Zarcas, Costa Rica.
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Here's a slightly longer section of call from an individual near Caño Negro, Costa Rica.
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Giant Toad call from Caño Negro, Costa RicaAnd here's my only recordings of Texas Giant Toads. This is a chorus of individuals calling from a resaca in Hidalgo County, Texas.
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Giant Toad call from Hidalgo County,
Texas

Stauffer's Treefrog (Scinax staufferi) is a common small frog over much of Eastern Mexico down through central America to northern Costa Rica. They are usually brown in overall all color and may have a pattern of darker brown spots. Like other Scinax, they have rather elongate bodies and a relatively pointed nose.

They call from the grassy edges of ponds and flooded ditches.The call of Stauffer's Treefrog is a short rasping buzz. Here's a recording from east-central Campeche, Mexico.

Looking at the spectrogram for a few calls we can see that the buzzy call is level in pitch and has two major dominant frequencies. We can also see how the two frogs calling here alternate the pitch of their calls to stand out from their neighbors.

The Yucatecan Casque-headed Frog (Triprion petasatus) is a good example of where old sayings sometimes fall short. The old adage goes "if it looks like a duck and sounds like a duck, its a duck". But this is a case where an animal that looks and sounds like a duck....is actually a frog!These strange duck-billed treefrogs is restricted to the Yucatan Peninsula where they are quite common during the rainy season. They can be found on roads and trails at night and their calls can be heard from any wooded area.

Their bizarre head ornamentation ("casque") is actually composed of bony shelves and ridges of the skull which are fused to the cranial skin. They not only have a duck-like beak, but there is a bony ridge coming forward from each eye towards the midline of the skull.

The function of this bony ornamentation is unknown but it has been hypothesized that these frogs use these bony plants to block their burrow entrances during periods of inactivity.

These strange duck-billed treefrogs have an equally strange breeding method. Because they live in the porous karst limestone of the Yucatan platform, there are few areas where water naturally stands on this porous ground. These treefrogs have adapted by laying eggs in any pool of standing water. We found the frog below calling from above a small hollow in a tree, no more than 2 inches in diameter and a few inches deep. He was trying to attract a female to lay eggs in that small temporary pool that had formed in that tree hollow three feet off the ground.

Triprion tadpoles are as strange-looking as their parents. Fairly early in development they get these bony casque structures on their heads and they are visible even in the tadpoles.The problem with nesting in pools in rocks or tree holes is that there isn't much nutrition available for the developing tadpoles. We observed these tadpoles in a water filled depression in a limestone rock. The depression was only a few inches deep and we observed the tadpoles feeding on each other. You can see some tadpoles feeding on another individual in this video towards the end. This tadpole cannibalism is common in other frogs that nest in ephemeral water bodies as well.

Just as you would imagine from a "duck-like" frog, the call is a nasal duck-like quacking. Here's an individual from near the town of Pisté, Yucatan, Mexico.
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And here's a small group, also from south of Pisté, Yucatan, Mexico.
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The two US toad species that are probably confused more than any others would have to be the American and Fowler's Toads (Anaxyrus americanus vs. Anaxyrus fowleri).

The problem is that they overlap in range across much of the eastern/northeastern half of the US and that they occupy much of the same habitats. They are both highly variable in color pattern and there is significant overlap in their characteristics. These two toads are confusing and difficult to tell apart even for experienced herpetologists (people who study reptiles and amphibians).

Fowler's ToadCherokee County, Texas

American ToadScott County, Arkansas

One thing that can be helpful occasionally for distinguishing the two species is that American Toads cansometimes have a reddish ground color. Fowler's Toad is usually gray/brown/black without the reddish tint. However, many American Toads do not have this reddish coloration and some Fowler's do. So if you find one of these two species and it is very reddish, it is probably an American Toad,...maybe. (It should be noted that other toads can be reddish, so not every reddish toad is an American Toad, it is just less likely to be a Fowler's Toad.)

One character that is often quoted in comparisons is the number of tubercles ("warts") in each of the dark spots on the back. If it has only a single (or two) warts in each dark spot, it is probably an American Toad. If it has three or more in some of the spots, it is probably Fowler's Toad.

Another characteristic used to "differentiate" them is the contact between their parotoid glands (big gland behind the eye on most toads) and the bony cranial ridges behind the eye. In American Toad there is a small spur on the cranial crest behind the eye that points posteriorly and touches the front of the parotid gland. You can see the small spur connecting the cranial crest to the parotoid gland in this American Toad from North Carolina.

American ToadNorth Carolina

In Fowler's (and Woodhouse's) Toads, the spur is usually missing and the parotid gland bumps right up against the transverse part of the cranial ridge. There is a nice diagram of this from the Frogs of Tennessee page here -

Another character that is sometimes mentioned is the color of the underside of the toad. American Toad is whitish underneath while Fowler's Toad can have some dark spotting particularly near the throat and front limbs.

Yet another characteristic that is used to distinguish them is the size of the tubercles (warts) on the tibial part of the leg. American Toad has prominent "warts" here while Fowler's are less noticeable and not larger than the rest of the leg tubercles.

So by looking at the tibial warts, cranial crests, parotid glands, belly coloration, and warts-per-spot on the back, you might be able to identify one of these toads to species. But these variables are hard to see in some individuals and apparently vary between species as well!

Now, in Texas the American Toad has a very limited range so the area of possible overlap is fairly small. These two species (and maybe Woodhouse's Toad) would only be expected to occur together in the counties of far NE Texas. The area of overlap is not completely defined as the known range of the American Toad in Texas is rather spotty.

So the experts can sometimes have difficulty telling these species apart, so

1. how do we tell them apart?

and

2. how do we know they are two species?

Well, the answer to both of those questions is their calls. Frog calls serve as reproductive isolating mechanisms. They generally prevent species from interbreeding. A female American Toad is not likely to be attracted to or approach a male Fowler's Toad because their calls sound so different.

Fortunately for us, we can also use these calls differences to identify which species of toad we are dealing with.

Both species have typical toad-like trilling calls. The difference is the length and tone of the calls. Fowler's (and Woodhouse's) Toads have short, buzzy, nasal trills that rarely last more than 3-4 seconds.

American Toads have a similar trill that is "cleaner/prettier" and a little less nasal sounding and often last between 5 and 30 seconds or more.

Here's a spectrogram comparing the two call lengths (American Toad on top, Fowler's on the bottom). You can see the American Toad trill continuing for almost 14 seconds while the Fowler's tapers off within 3 seconds. You can also see that the Fowler's Toad call is "messier" on the Y axis (frequency axis). This tells you the call will be buzzy rather than the clean almost single pitch call of the American Toad.

And here's what that difference sounds like. These 15 second recordings include a single call by an American Toad while the same time period includes three calls of Fowler's Toads. The difference is so obvious that in spite of their physical similarities, you aren't likely to confuse a calling American and Fowler's Toad.

First the long pretty, whistled trill of the American Toad:

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then the short, buzzy, nasal trill of the Fowler's Toad. :

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Next year, I hope to be able to post an American Toad recording from Texas.

The American Toad (Anaxyrus americanus) is a widespread and well-known toad of the northeastern United States.

Here in Texas however it has a much more restricted range. It is only known from a few counties in north-eastern part of the state. It's range in Texas isn't fully understood because it is very difficult to distinguish from the more common Fowler's Toad.

I still haven't seen an American Toad in Texas :-( so these photos and this recording come from nearby Arkansas.

In many areas of the northeastern US, this is a common "yard toad". They are variable in general color ranging from brownish-black to bright reddish. They often have dark spots on their back. There is usually a light mid-dorsal stripe visible and a lighter stripe running from the tympanic membrane (ear) down towards the hind leg. These lighter stripes are sometimes obscured by the ground color.

American ToadFairfield County, Connecticut

American ToadNorth Carolina

Our Texas and nearby populations of American Toad are smaller than the typical American Toads of the Northeastern US and have been identified as belonging to a separate subspecies, the Dwarf American Toad (A. americanus charlesmithi).

Dwarf American ToadOuachita County, Arkansas

They breed in spring into early summer. When they breed successfully, you can often find their distinctive helical strings of black eggs in nearby ponds and streams.

American Toad EggsScott County, Arkansas

The call of the American Toad is a very long, high-pitched trill. It lasts from 5 seconds to over 30 seconds. The Dwarf American Toad subspecies has a slightly higher pitched call than the typical larger northeastern subspecies.

Here is an American Toad from the Ouachita National Forest in Arkansas calling from the middle of a forest road low water crossing.

Rio Grande Leopard Frogs (Lithobates berlandieri) will usually call while floating in shallow water. Their vocal sacs protrude laterally from the sides of their heads. This individual was calling from a flooded riparian area underneath a bridge in McMullen County, Texas.

Here is a recording of a Rio Grande Leopard Frog from Bexar County, Texas. It's call could best be described as a series of "croaking" calls.
The higher pitched clicking heard behind the Leopard Frogs are the calls of Blanchard's Cricket Frog Acris blanchardi

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This spectrogram represents the first three "croaks" of the preceding call.

2016 Addendum -

Like most frog species the sound of the call of the Rio Grande Leopard Frog can change with ambient temperature. At lower temperatures, the tempo of the snoring call slows down and sounds a bit different.
You can hear that by comparing these calls from one of my favorite roadside ponds near Quihi, Texas.

One summer evening in August I stopped by there to record some Rio Grande Leopard Frogs along with other species. Here's what they sounded like in this warm shallow pond at an air temperature of 75°F (and a water temperature probably a bit higher than that) -

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I returned to this pond on a cool winter evening (for south TX that is) after it had rained heavily and was 56°F. The only species calling that night was the Rio Grande Leopard Frog.

Notice how much less "snore-like" it sounds.

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Most of my frog recordings are made in mono. There is only a single channel of the recorded call and it plays exactly the same over the left and right speakers. The reason for this is that I generally use a shotgun microphone to help isolate individual frog calls and most shotgun microphones do not capture stereo. Furthermore, when trying to focus on an individual frog you are recording sound coming from what is in all practicality, a point source. Because the sound is coming from a single point, there is no difference in what it sounds like coming from the left and the right. But we normally hear in stereo because they have two ears on the opposite sides of their head. Most sounds coming towards your head are picked up by both ears, but sounds coming from the left side reach the left ear slightly sooner than they do the right ear. Yes, the difference in arrival time is very small at the speed of sound, but there is a difference.Furthermore, your head blocks some of the sound coming from the left side as it moves over to the right ear. So the right ear receives the sound slightly later and slightly less loud. Your brain is able to interpret these differences in arrival times and volume to give you a stereoscopic auditory image.To some degree, the relative asymmetry of the pinnae and auditory canals also allows you to differentiate sounds coming from above and below as well. So by comparing the signals between your right and left ears, you can localize where a sound is coming from in space. (It is more complicated that this as studies have shown that it isn't simply the position of the ears that determines individual's ability to discriminate the source of a sound. - for example, Claes, et al., 2015).
So your perception of space in the auditory landscape is dependent on the position of the sound source and the difference in arrival time and intensity at each ear and the ability of your brain to assimilate and interpret that information correctly.

Localizing Space in Recorded Sounds

But now stop and think about listening to a recording. For simplicity, let's imagine you are wearing headphones and listening to a stereo recording. The relative position of the speakers does not change so to your ears, the sound source for each ear is the same. Furthermore, your left ear and right ear are hearing different recordings (tracks). Therefore, the only mechanism you have for localizing the source of a sound is to compare the sound arriving in each ear and extrapolate distance information from those differences.Here's a simple demonstration of how this works.Here is a recording of a Cajun Chorus Frog
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It is playing exactly the same recording in both of your ears (both channels) therefore you can't localize where the sound is coming from or your brain will tell you it is coming from right in front of you.Now listen to this version of exactly the same recording. In the first call, the frog is clearly in the center. In the second it sounds like it is coming from the right and in the third it is coming from the left.
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So why does it sound different? It isn't just a matter of me turning down the signal from the left then right speakers. The sound is coming into both speakers. You can prove this to yourself by removing the headphone from your left ear and just listening through the right ear and vice versa.So why does exactly the same recording sound like the frog has moved from the center to the right and to the left? Simple. I took the two channels of the mono recording and added an extra 1/1000th of a second of silence in front of the left channel in the middle call and the right channel in the last call. So at first the two channels are playing simultaneously, then during the second call the left channel is playing 1/1000th of a second later than the right, and in the third call the right channel is playing 1/1000th of a second later than the left. So when the sound is getting to your right ear a fraction of a second later your brain tells you the sound is "coming from" your left.Last little bit of brain trickery....now listen to this frog (again same original recording).

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It starts off in front of you but gets further and further away to the left with each call. Of course the frog and your speakers aren't moving. The first call is arriving at both ears simultaneously and at equal volumes. The last three calls are arriving 1/1000th of a second later to the right ear (putting the frog on your left) and then each subsequent call is reduced in volume on the right channel 1db. Your brain interprets that reduction in sound in the right ear relative to the left as a measure of distance.So your brain is localizing the position of a sound source by the difference in arrival time and volume between your ears. Of course, your ears (pinnae) point forward on your head, so you can actually differentiate whether sounds are coming from behind your or in front of you (sounds in front of you will sound louder). Therefore sophisticated sound systems often rely on 5 or even 7 speakers to create that sense of sound localization called surround sound.

Recording in Stereo

Recording sounds in stereo is really a bit of trickery. You have to record the sounds in such a way that the human ears will feel like they are there in the actual environment. So you have to control the timing and volume of the sound coming into each microphone in such a way to approximate the experience the listener would have had in the field.This is achieved by using multiple microphones and positioning the microphones so you can control the timing of the arrival of sound to each microphone. Some of the different mechanisms have involved positioning two microphones close to each other but facing the opposite directions (at various angles), facing each other at various angles, spaced apart different distances, etc., etc., etc. Then there are the various methods of baffling the sound between the two microphones in order to approximate the effect of the human head. Other approaches have included things like making fake heads and putting mics in the ears. There are lots of good discussions of the pros and cons of different methods online.One popular approach among nature recordists is to place the microphones in an arrangement called a SASS (Stereo Ambient Sampling System) array. This type of arrangement is known for producing a realistic stereo effect and also has the added advantage of amplifying the signal at the same time. Vicky Powys has a great discussion of SASS and how it works for field recording on her wonderful blog, the Capertee Birder.

My Stereo Setup

My first forays into stereo recording were accomplished by unplugging my shotgun microphone from my Olympus LS-10 or LS-11 recorders and recording using the XY stereo microphones which came on the recorder itself. Here is a recording of a chorus of Hurter's Spadefeet calling from a flooded area in DeWitt County, Texas.
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This gave a satisfactory stereo image and you can clearly hear that the sounds are coming from two sides. But the image is rather "narrow". The frogs don't seem to occupy much space in the auditory landscape. I found myself wanting to get a better sense of space and more amplification. Inspired by examples built by Vicky Powys, I decided to make my own "field hardy" SASS unit. Of course, I am not any kind of handyman and the idea of cutting wood at precise angles, etc., was very unappealing. So I decided to try to make a "sort of" SASS unit out of a dense foam Yoga Block. I downloaded the SASS dimensions from Vicky's blog and shrunk them down to fit on the largest yoga block I could find and I made my unit from there. After I made it, I was happy to see that Curt Olson had already established that smaller units will provide good stereo images.

My SASS array isn't pretty (I'm wondering is I shouldn't call it the HALF-sASS ;-)). But it does give me a much better stereo image as well as a boost in gain (volume). And I invested all of about 20 minutes making it and $4 for the Yoga Block. Furthermore, it is one unbreakable piece and only weighs 5oz (142 grams) total so it is great for travel.The green foam in the "nosepiece" is intended to allow a bit more sound to pass between the left and right sides than the dense foam of the yoga block. The nosepiece is essentially hollow but blocked with that more open foam (I just hollowed out the center with a knife). The pink things sticking out under the microphone are sections of rubber bands that hold the microphones flush in place at the edge of the yoga block (without these, the mics are a bit loose and too easily pulled out while positioning the unit). The blue rubber band is just to hold the excess microphone cable out of the way while in use. I thought about attaching a tripod screw or quick release plate, but I generally just put it on the ground, a stump or even hold it in my hands for shorter recordings.For microphones I use a stereo pair of small EM-172 based microphones I bought from Micbooster.com. These EM-172 mics are very popular among nature recordists for being very quiet. You could buy the small mic capsules yourself and make your own microphones for less money but as I said, I am not handy and the Micbooster set comes pre-assembled - no soldering required!The results from the SASS array are much more pleasing to my ear. This is a chorus of several species of frog (Gray Treefrogs, Spring Peepers, Cajun Chorus Frogs and Southern Leopard Frogs) in Davy Crockett National Forest in East Texas in March, 2016 with version I of my foam SASS unit. You can hear how much more "width" there is in the recording and I think an improved sense of space. I am not sure there is enough center in the stereo image so I think some modifications might be in order once I do some research.
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To try and give me a better "center" image to my stereo recording, I have also been experimenting with the the ORTF technique (named for the Office de Radiodiffusion-Télévision Française who developed it). For this technique two cardioid microphones are place 17cm apart (approximating the distance between the human ears) and at 110° angles to each other. To my ear, this produces a more natural stereo sound that better approximates the experience you hear in the field. Here's an ORTF recording of a chorus from Guadalupe County, Texas in February 2017 (Cope's Gray Treefrogs, Blanchard's Cricket Frogs, and Southern Leopard Frogs) -
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Frogs in Stereo - Is it worth it?

Of course, this begs the question "Is it useful/valuable to record frog choruses in stereo?". There are two issues with this:1. A frog chorus is generally fairly localized to a small area such as a small pond or drainage ditch. If you are any distance from this source you really don't get much stereo image since all the calls are effectively coming from one spot.2. If you do get a large area or get close to the chorus, the sounds coming from each side/area are roughly the same. So even though there is a difference in timing and volume in the stereo image you don't get as much sense of space due to the uniformity across the space. Here's an example of a situation where recording in stereo adds very little to the ambience of the recording. This was a very loud chorus of Mexican Spadefeet, Texas Toads and Spotted Chorus Frogs in Schleicher County, Texas.Here's the stereo version
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And here's the mono version of exactly the same recording.
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You can hear that there really isn't a huge difference in sound between the two. So recording this in stereo probably wasn't necessary.In contrast, when there are fewer frogs more widely spaced, such as these Canyon Treefrogs in the Davis Mountains of West Texas, a stereo recording does add more "information" to the recording.Here is a stereo recording of these Canyon Treefrogs. You can tell where they were in space and which ones were closer to the recorder (Olympus LS11 by itself in this case).
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And here is the same recording recorded to mono. I think you can agree there is a loss of auditory information in this recording.
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In the right situations, stereo recordings of frogs can add a lot to your sense of "being there" which is really the point of any amibence recording. It is a bit more work to get a good stereo recording, but when it works it is worth the effort to capture the essence of the "frogscape" you experienced.